Low-dispersion glasses are useful optical glasses employed as materials in various optical elements. For example, Japanese Unexamined Patent Publication (KOKAI) Showa No. 60-171244 discloses low-dispersion glass having an Abbé number (νd) of about 60 to 73. On the other hand, the widespread popularity of image pickup devices such as digital cameras and portable telephones equipped with cameras is increasing the demand for size reduction in image pickup optical systems based on configurations of small numbers of lenses. This has been accompanied by an increase in demand for aspherical lenses.
Precision press molding is known as a method for mass producing, with good productivity, optical elements such as aspherical lenses that are expensive to manufacture by grinding and polishing. Precision press molding requires glass that softens at low temperature and has good weatherability. Conventional low-dispersion glasses have poor weatherability and cannot be employed in precision press molding.